fix: process-messages script not working when hidden file is auto-created

e.g. .DS_Store on macos

packages/svelte/scripts/process-messages/index.js

@@ -9,6 +9,8 @@ const messages = {};
 const seen = new Set();
 
 for (const category of fs.readdirSync('messages')) {
+	if (category.startsWith('.')) continue;
+	
 	messages[category] = {};
 
 	for (const file of fs.readdirSync(`messages/${category}`)) {